Epigenetics and Behavior

by

Eva Jablonka, Zohar Bronfman

• LAST REVIEWED: 29 April 2015
• LAST MODIFIED: 29 April 2015
• DOI: 10.1093/obo/9780199941728-0063

Introduction

Behavioral epigenetics is part of the thriving field of epigenetics, which describes the study of developmental processes that lead to persistent changes in the states of organisms, their components, and their lineages. Such developmental, context-sensitive changes are mediated by epigenetic mechanisms that establish and maintain the changes in patterns of gene expression and cellular structures that occur during ontogeny in both nondividing cells, such as most mature neurons, and dividing cells such as stem cells. When information is vertically transmitted to cells during cell division, or horizontally between cells through migrating reproducing molecules (like small RNAs), and when variations in the transmitted information are not determined by variations in DNA sequence (i.e., the same DNA sequence has more than one cell-heritable epigenetic state), epigenetic inheritance is said to occur. Behavioral epigenetics investigates the role of behavior in the shaping of developmental epigenetic states and the reciprocal role of epigenetic factors and mechanisms in the shaping of the behavior of human and nonhuman animals, at the short-, middle-, and long-term (ontogenetic, ecological, and evolutionary) time scales. The focus is on the molecular-epigenetic study of the interactions between environmental factors, such as ecological factors and habitual activities such as lifestyles and learning, with genetic variation and the neurobiological and physiological mechanisms that mediate between the regulation of gene expression and behavior. This range of epigenetic processes therefore includes, but is not limited to, studies involving epigenetic inheritance and the direct and indirect evolutionary effects of epigenetic developmental mechanisms. The neural-behavioral aspects that occur during ontogeny through the mediation of epigenetic mechanisms are central to behavioral epigenetics and are the main focus of neural epigenetics.

Epigenetic Mechanisms

The major types of epigenetic inheritance systems that have been recognized are (i) Self-sustaining loops involving, for example, positive regulation of a gene’s activity by its products, which leads to the maintenance of a pattern and activity and that, when transmitted during cell division, cause the same state of gene activity to be reconstructed in daughter cells. (ii) Structural templating, in which three-dimensional cellular structures act as templates for the production of similar structures, which then become components of daughter cells. The structural templating involved in the propagation of prions is an example of such a mechanism. (iii) Chromatin-marking, in which patterns of DNA modifications such as attached methyl group (CH₃) and modifications in the histone proteins associated with DNA are reconstructed during cell division. Chromatin marks can be dynamically maintained over a long time. In dividing cells, some hitchhike on DNA replication and segregate, with parental marks nucleating the reconstruction of similar marks on daughter DNA molecules. The different chromatin marks are functionally and mechanistically related and often work synergistically. (iv) RNA-mediated systems, in which small transmissible RNA molecules regulate translation and transcription through interactions with mRNA or DNA to which they are complementary. As described by Jablonka and Lamb 2014, the long-term developmental maintenance of states that are regulated by small RNAs can occur through several different mechanisms. Small ncRNAs can migrate from cell to cell, so silencing can spread horizontally within an organism (Hoy and Buck 2012). These mechanisms operate and interact in all cells, including the nervous system, and have been shown to be central to the nervous system’s development and functions.

• Hoy, A. M., and A. H. Buck. 2012. Extracellular small RNAs: What, where, why? Biochemical Society Transactions 40:886–890.

  DOI: 10.1042/BST20120019

  This paper provides an overview of the properties of extracellular miRNAs in relation to their capacity as biomarkers, stability against degradation, and mediators of cell–cell communication.

• Jablonka, E., and M. Lamb. 2014. Evolution in four dimensions: Genetic, epigenetic, behavioral, and symbolic variation in the history of life. Cambridge, MA: MIT.

  An accessible monograph, discussing the many aspects of epigenetic inheritance and highlighting its evolutionary implications. Behavioral epigenetics is discussed at length in chapter 11 of the revised edition. Originally published in 2005.